Smoking is associated with pneumonia development in lung cancer patients

Background Various host factors can promote pneumonia susceptibility of lung cancer patients. However, data about risk factors for pneumonia in lung cancer patients receiving active treatments such as chemotherapy, radiotherapy, and surgical intervention are limited. Thus, the purpose of this study was to identify risk factors for pneumonia development in lung cancer patients. Methods The present study used a lung cancer cohort of the Catholic Medical Center at the Catholic University of Korea from January 2015 to December 2018. Pneumonia was defined by the presence of a new or progressive infiltration on chest imaging together with any of the following: new onset purulent sputum, change in character of chronic sputum, and fever. We ruled out noninfectious infiltration such as drug or radiation toxicity and hydrostatic pulmonary edema. We especially excluded those if computed tomography revealed sharp demarcation consolidation or ground glass opacity limited radiation field. Results A total of 413 patients were enrolled in this study. Pneumonia occurred in 118 (28.6%) patients. The pneumonia group had significantly worse overall survival (OS) than the non-pneumonia group (456.7 +/- 35.0 days vs. 813.4 +/- 36.1 days, log rank p < 0.001). In patients with pneumonia, OS was shorter in ex-smokers and current smokers than in never smokers (592.0 +/- 101.0 days vs. 737.0 +/- 102.8 days vs. 1357.0 days, log rank p < 0.001). Age (hazard ratio [HR]: 1.046; 95% confidence interval [CI]: 1.019-1.074; p = 0.001), clinical stage IV (HR: 1.759; 95% CI: 1.004-3.083; p = 0.048), neutropenia (HR: 2.620; 95% CI: 1.562-4.396; p < 0.001], and smoking (HR: 2.040; 95% CI: 1.100-3.784; p = 0.024) were independent risk factors of pneumonia development in lung cancer patients in multivariate analysis. In subgroup analysis for patients treated with chemotherapy, age (HR: 1.043; 95% CI: 1.012-1.074; p = 0.006), neutropenia (HR: 3.199; 95% CI: 1.826-5.605; p < 0.001), and smoking (HR: 2.125; 95% CI: 1.071-4.216; p = 0.031) were independent risk factors of pneumonia development. Conclusions Smoking and neutropenia were risk factors affecting pneumonia development in the total group and subgroup of patients with lung cancer.